Updated at 10:09 a.m. Eastern:
Iraqi security forces blocked streets around the capital Monday and conducted intense searches at checkpoints as authorities investigated the massive security failure that allowed two truck bombs to strike what was supposed to be one of the city's safest areas and kill 155 people.
The country's worst attacks in more than two years on Sunday targeted the Justice Ministry and Baghdad Provincial Administration in the heart of the capital, calling into question Iraq's ability to protect itself as it prepares for January elections and the U.S. military withdrawal.
Dr. Salah Abdel Razaq, Baghdad's governor, was in his office in the provincial council building when the bombs went off. More than 100 of his colleagues were injured, most by flying shards of glass. One colleague, a senior prosecutor for the capital city, was blinded in both eyes by glass from the shattered windows.
"The bodies I have seen - these innocent people, what they have done?" a bewildered Razaq asked CBS News correspondent Elizabeth Palmer on the phone. "To have this destiny, it is very terrible."
Fear of more deadly attacks, especially in the run-up to crucial January elections, turned into anger over the government's failure to keep the country secure.
"Today, we came to work despite the fear inside us," said Siham Abdul-Karim, 49, an employee of the Culture Ministry located near the site of the bombings and surrounded by police checkpoints on Monday. "We all wonder how could car bombs could reach these institutions."
There have been no claims of responsibility, but massive car bombs have been the hallmark of Sunni insurgents seeking to overthrow the country's Shiite-dominated government. It was the second deadly bombing targeting government offices in the area since August, when coordinated blasts against two ministries killed more than 100 people.
Palmer reports that many in Iraq believe the radical Sunni militants behind Sunday's attack had help from disaffected loyalists to Saddam Hussein's Baath party, who resent the country's Shiite-dominated government.
"Suicide -- this is the method of al Qaeda," Dr. Razaq told Palmer, "but they have been supported logistically by the Baath party."
The death toll rose to 155 on Monday as Baghdad residents buried the dead. About 500 people were injured, authorities said.
The initial investigation suggested the vehicles, each packed with thousands of pounds of explosives, might have passed through some security checkpoints before hitting their destination, said Maj. Gen. Qassim al-Moussawi, a spokesman for the city's operations command center. Authorities have said they are also checking security cameras in the area.
Interior Minister Jawad al-Bolani said 76 people have been arrested so far, but he did not provide information on who they were or how they are believed to be connected to the horrific crimes, which took place just hundreds of yards from the heavily fortified Green Zone.
"This is a terrorist act," al-Bolani said. He called on all the political forces to cooperate and assist the Iraqi security forces.
The street where the blasts occurred had just been reopened to vehicle traffic six months ago. Shortly after, blast walls were repositioned to allow traffic closer to the government buildings - all measures hailed by Prime Minister Nouri al-Maliki as a sign that safety was returning to the city.
Al-Maliki has staked his political reputation and re-election bid on his ability to bring peace to the country but as grief turned into anger on Monday people questioned the government's recent security policies - ominous signs for al-Maliki's re-election bid.
"This explosion made people furious," said Ahmed Hassan, an employee at the Ministry of Education. "People will not re-elect this government."
The pickup truck that exploded near the Justice Ministry was carrying 2,205 pounds of explosives, the initial investigation found. The second pickup truck that went off near the Baghdad Provincial Administration building, was carrying 1,543 pounds of explosives.
The explosives were attached to the vehicles and hidden below the seats, al-Moussawi said.
Iraqi health and security officials confirmed the death toll. They spoke on condition of anonymity because they were not authorized to release information to the media.
Sen. John McCain Sunday that the attacks should not cause the United States to delay withdrawing American troops from Iraq, adding that he believes such violence will continue.
The Arizona Republican said the attacks indicate that improving the situation there is a slow process and a "terrible tragedy." He blamed extremists trying to ignite sectarian violence, but said that while such attacks continue, "they are not sustainable.
"The majority of the people are opposed to them. And the Iraqi military will be able to handle this transition. But it's not going to be without tragedies such as we've seen just today," he added.
The coordinated bombings were the deadliest since a series of massive truck bombs in northern Iraq killed nearly 500 villagers from the minority Yazidi sect in August 2007. In Baghdad itself, it was the worst attack since a series of suicide bombings against Shiite neighborhoods in April 2007 killed 183.
Also Monday, a car bomb at a police checkpoint near the holy city of Karbala in southern Iraq killed at least four people, Iraqi security officials said on condition of anonymity because they were not authorized to speak to the media.
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